I'm currently writing a small cross-platform OpenGL-based 2D game engine for our studio. When I researched which 2D Vector class to use, I stumbled across three different design paradigms:
Double & Call-by-reference. If I understand the above article right, I could also use 2 double precision variables instead of the 4 float numbers. According to the above thread double's still slower than float.
Template for double and float: The widely popular book "Game Engine Architecture" uses templates to make it possible to use float and double as needed. The obvious downside is code bloat. Also, I doubt it that the code can be optimized without basically writing two classes, anyway.
I would appreciate to learn what solutions you're using in your in-house engines and how precise e.g. popular game engines are, so I can decide what solution I'll implement in our engine. In the moment I'm thinking about simply using float precision and live with it.